| 摘要 |
PURPOSE:To raise the accuracy and the stability for measuring the dust concentration and to display abnormal concentration by preventing the dust form adhering a light emitting device and a light receiving device, and also, controlling their operating temperature, and moreover, deciding the abnormality of the light transmittivity. CONSTITUTION:Air is led into a container 18 through a pressure reducing valve 32 and an air filter 34, and allowed to flow to a passage 20 through a pin hole 24 of a partition plate 26. Subsequently, a light receiving device 12 provided with a photodiode (PD) is irradiated by a light beam from a light emitting device 10 provided with a light emission diode (LED), and a pulsative photocurrent is generated in the PD. A variation of the photocurrent caused by dust is converted to a light transmittivity signal and inputted to a deciding circuit 40, and when the transmittivity drops to a reference value or below, a signal for showing an abnormal state of dust concentration is displayed on a display device 42. Also, operating temperatures of the LED and the PD are held at a set temperature by temperature controllers 46, 48. |
